Volume control for radio amplifier circuits



Dec. 29, 1931. o. E. MARVEL 1,839,109

VOLUME CONTROL FOR RADIO AMPLIFIER CIRCIJITS Filed July 15, 1927 Jl M n v w w \m a k w S N Q My W" R mm Ill! 1 Mu u i Q H \3 V n Q g u INVENTOR.

ATTORNEYS.

Patented Dec. 29, 1931 UNi-rsofsrATEs PATIENT, OFFICE."

- 03m E. MARVEL, or DAYTON, onto, AssIGNoR, BY MESNE ASSIGNMENTS, TO GENERAL iuo'rons RADIO CORPORATION, .OFVDAYTON, onro, A oonronerronor OHIO VOLUME oon'raor. FOR RADIO AMPLIFIER CIRCUITS A Application filed. July 15, 1927. Serial No. 206,068.

The present invention relates to improvements in the arrangement and connections of the circuits ofan electrical. apparatus adapted for the generation, reception ..or

5 transmission of electrical currentoscillations of varying, frequencies. 7

One object of this invention is toprovlde in an apparatus of the above type a'slngle control whichis connected to a plurality of 10 circuits to regulate the volume of the signal produced, the arrangement being suchthat the volume of the signal may be regulated when receiving signals from either distant or nearby sources without interfering with '15 the quality of the signal. 1 r

Further objects and advantages of thei nvention will be apparent fromthe following description when taken in connectionwith the accompanying drawings illustratingone embodiment of the, present invention in which a w it ig. 1 is a circuit diagram of aradio re.- ceiving apparatus of my invention; and r Fig. 2 is an enlarged circuit "diagram showing the essential features of a 'partof The apparatus selected as illustrative of my invention is a radio receiving set having an .untuned antenna circuit adapted to receive signal current oscillations of different frequencies, to which circuit there are connected in cascade a series of electron devices or audionsindicated by the reference characters 21, 22, 23, 2a, 25 and 26 respectively. Each of the dischargei devices comprises, in the embodiment shownin Fig. 1, a cathode 30, a plate electrode or anode 31, anda grid electrode 32 interposed between the cathode and the anode. Each discharge device or audion is also provided with a .heatedfilament '33 whichis connected to asuitable source as thealternating: current source 3% a to maintain the cathode. at

rent 34- or to any other suitable source of through a condenser 37 r i 23 are coupled together andito the detector the proper temcurrent, and the cathode elements 30 are in.- terconnected through a connection '35 which is connected to the common groundwire 36 l The radiofrequencyamplifiers2l, 22 and 24 by means of suitable radio frequency transformers 40, 41 and 42 respectively, each having suitable inductively coupled primary and secondary windings. The detector 24 and the audio frequency amplifiers 25 and 26 are coupled together by means of the two audio frequency transformers 43 and 44;. The grids 32 of the audions 22 to 26 inclusive are each connected with the secondary windings of the next proceeding transformers, whereas the grid electrode of the first'audion 21' is connected to the antenna circuit, preferably 'by means of the close coupling of the type illustrated.

i The plate electrodes 31 of the audions 21 to 25 inclusive are each connectedwith thep'rimary, windings of the transformers or cou plings by which these audionsare' coupled to the succeeding audions, while the plate of translating device suchas a loud speaker 48, with a suitable source of current As illustrated said plate circuits are connected with suitable sources of energy of the proper po tential, the platecircuits of audions 21, 22 and 23 being interconnected at the point 49 r and connected through a resistance with the positive terminal 13-!- of thesource or B battery 5O as indicated at 53. The negative terminal B of the B battery, is connected through the 0 battery 51 to'the ground 52, which as previously-explained is connected through. the condenser 37 to the common cathode connection 35.to complete the plate circuits. The plate circuits of detector-tube 24 and of the audio amplifiers 25 and 26 are connected with the B battery 50 as indirated at 54, 53 and 55 respectively, so that the proper voltage will be supplied to these various audions.

' The grid circuits of each of the audions 21 to 26 inclusive are connectedthrough the C battery 51 to the common cathode wire 35 so that suitable negative potentials are' im- I? theaudion 26 is connected through asuitable V pressed upon the grids of the amplifiers 25 and 26. As shown one of the radio frequency tubes has its output circuit controlled by a switch 46 which may be manually closed to place a reactance 47 across the transformer winding.

4 The grid circuits of the radio frequency amplifiers 22, 23 and 24 are each provided with an adjustable capacity 58' in parallel with the transformer secondaries so that these circuits may be adjusted to resonance with the incoming signal oscillations to be amplified; and the grid circuit of the detector tube 24 is also provided with the condenser and grid leak elements 57 customarily employed in the grid circuits of'detector tubes. In the apparatus set forth in Fig. 1, the tuning condensers 58, which are connected across the secondary windings of the transformers a0 and ll, are also provided with balancing plates 59 connected to the proper point 60 of the next succeeding transformer secondary so that a suitable amount of energy may be fed back from the succeeding grid circuit opposing the energy in the proceeding grid circuit to maintain these grid circuits at a substantially constant or negligible effective resistance as set forth in my prior application Serial Number 205,739, filed July 14:,

1927, entitled Electrical apparatus.

The plate 31 of the audio frequency amplifier 25 is connected to the primary winding of the audio frequency transformer 44 through a condenser 61 and is also preferably connected to a choke 62 connected across the primary as shown. One side of the primary of this transformer is connected through a wire 63 to one end 64 of a potentiometer or resistance 65. This resistance is provided with an adjustable contact 66 which may be moved along the length of the resistance and which may be manually adjusted as desired. This movable contact 66 is connected through the wire 67 to the other side of the primary winding of the transformer 44 so that by moving the contact to the left (see Fig. 1), a low resistance shunt path is provided across the primary of this transformer to control the volume of signal supplied to the transformer and consequently to control the volume of the signal received in the speaker 48. Then the contact 66 is moved to the right to the end of the resistance the shunt path across the primary of the transformer will be of sufficiently high resistance so that the power supplied to the transformer from the plate will not be materially affected. The resistance of the element 65 is preferably of the order of about 20,000 ohms (as distinguished from one of several million ohms), so that when the full resistance is applied across the primary of the transformer the latter may operate at substantially its maximum eficiency.

The potentiometer or control resistance 66 is also utilized to vary the potential of the plates or anodes of the radio frequency tubes 21, 22 and 23 which are connected at point 49 to the end 70 of resistance element 65. The variable contact 66 which is connected to one side of the winding of the transformer eat is also connected by the wire 71 to the positive side of the B battery 49. A variable resistance is thus interposed between the positive side of the B battery and the plates of the radio frequency tubes. When the adjustable contact 66 is closely acent the end 70 the resistance interposed between the B battery and the tube plates will be a minimum and consequently full B battery voltage will be supplied to maintain the potentials of the plates of these tubes at a proper high value so that they may operate at their maximum efficiency. However, when the adjustable contact 66 is moved toward the end G-lof the resistance the full resistance of the element 65 will be in series with the battery connection to the plates of the radio frequency tubes and the potential of the plates will thus be lowered so that the output of these tubes is somewhat reduced. The potential of the plates of the radio frequency tubes may thus be lowered to decrease the output of the radio frequency tubes at the same time the output of the audio frequency amplifier 25 is reduced by partially short-circuiting the primary of the transformer 44. On the other hand when the transformer 44: is operating at its full efficiency and the adjustable contact 66 is adjacent the end 70 of the resistance the output of the plate circuits of the radio frequency tubes also will be a maximum. By using a resistance of the order of 20,000 ohms it is thus'possible to provide for an eiiicient control of the volume of signal received from either nearby or distant sending stations and such a control is particularly desirable when the electron tubes are energized from an alternating current source since in this case a control of filament current to vary the volume is not easily accomplished. When receiving signals from nearby powerful stations the usual several milliamperes flowing in the plate circuits of the radio frequency tubes may be reduced to several tenths of a milliampere which is sutficient to provide for suitable operation of the radio frequency tubes. The use of a comparatively low resistance potentiometer having a resistance of the order of 20,000 ohms, however, permits the potentiometer to be made in a practical manner so that it may safely carry the several milliamperes required when the plates of the radio frequency tubes operate at their maximum efiiciency with full plate voltage applied to them, there being no likelihood of overheating or burning up of the resistance such as might happen if the potentiometer were of several million ohms resistance, it being a difficult or almost impossible matter to manufacture a very high resistance of this nature in small size so that it may carry this amount of current without overheating or burning P- v It is intended that my invention shall be susceptibleto usewith electron discharge devices such as shown in Fig. 2 in which the cathode is the heated electrode 80 of these tubes. The connections from the resistance 65 to the plates 31 of the radio frequency amplifying tubes 21, 22 and 23 is similar to that shown in Fig. 1, the movable contact 66 being also shown connected to the positive terminal of the B battery 50 and to the primary winding of the audio frequency transformer 4A, the latter being connected by the wire 63to the end 64 of the resistance element. The various connections of the filaments and the rest of the grid and plate circuits have not been indicated in this view and may be of conventional character.

It will thus be apparent that I have provided a single device which may be manually adjusted to suitably regulate thevoluine of output of a radio apparatus of thecharacter set. forth. The common resistance element 65 being connected in the plate circuits of the radio frequency tubes and also connected to place a variable path in shunt with a transformer winding operating at audio frequencies provides for suitable control of the signal in a simple manner.

While the method herein described and the forms of apparatus for carrying this method into effect, constitute preferred embodiments of the invention, it is to beunderstood that the invention is not limited to this precise method and forms of apparatus, and that changes may be made in either without departing from the scope of the invention which is defined in the appended Claims.

What is claimed is:

1. In a radio receiving apparatus, a plurality of separate associated circuits, a transformer winding in one of said circuits, the

other circuit including an output electrode of an electric discharge device, a'voltage source connected to an adiustable resistance, and

connections from said resistance to said transformer winding and said output electrode so that the output of the transformer may be decreasedsimultaneously with a change of potential of the output electrode.

2. In a radio receiving apparatus,a plurality of separate associated circuits, a transformer connected in one of said circuits,the other circuit being adapted to carry radio frequency currents and including the anode of an electron tube, a voltage source conto be increased simultaneously with increase of the output of said transformer.

nected to said voltage source, transformer,

and output electrode so as to simultaneously increase the voltage supplied from said voltagev source to said electrode and increase the efiiciency of said transformer.

5. In a radio receiving-apparatus, a plurality of separate anode circuits, a potential source in one anode circuit, a resistance in said anode circuit in series with said potential source, means for varying said resistance, a transformer associated with the other anode circuit, connections between said transformer and said resistance to provide a variable resistance in shunt with one side of said transformer for decreasing the output of the transformer as the anode voltage in the said one circuit is decreased.

6. In a radio receiving apparatus, an electron tube having a plate circuit adapted to carry radio frequency oscillations, an asso ciated circuit adapted to carry audio frequency oscillations and including one winding of an audiofrequency transformer, and volume control means comprising a common variable resistance element connected with both of said circuits.

7. Ina radio receiving apparatus, an elecs tron tube having an anode circuit adapted to carry'radio frequency. oscillations and including a source of potential, an associated circuit adapted to carry audio frequency oscillations and including the "primary winding of an audio frequency transformer, a resistance element, one end being connected to the said source of potential, the other end to one side of said winding, and a movable contact for said resistance element connected to the anode and to the other side of the winding of the transformer.

- 8. Ina radio receiving apparatus having a radio frequency anode circuit and an audio prising operating a single control member to simultaneously increase the anode voltage while changing the power supplied to a 195 windingrof the transformer. In testimony whereof I hereto aiiix my signature.

ORIN MARVEL.

. frequency transformer circuit, the method of controlllng the volume of said apparatus com 

